Proportions ('profiles') of the three main mouse T cell sets, Ly123:ly1: ly23, are characteristically distored in immune-deviant hairless (hr) mutant mice (higher Ly123: lower LY1), and after thymectomy (lower Ly123: higher Ly1). We propose to define these models further, especially in terms of Qa-1 subsets (because of the evident bearing of Qa-1 on suppression and immune regulation), in company with nu/nu athymic mice. Equal weight is given: (a) to elucidating various bases of immunodeficiency and deviation, genetic and non-genetic, and (b) to evaluating therapeutic agents: thymopoietin-TP5, ubiquitin, TCGF, - deficient, deviant and normal mice. In conjunction with tests of immune function in vitro, these immunogentic studies are intended as paradigms for investigating the nature and therapy of human disorders of immunity. New studies, with pleiotropic-mutant W mice, aided by the Ly-5 marker system, promise to extend immunogenetic analysis to pre-lymphocytic stem sets and to identify the reputed T cell said to collaborate in erythropoiesis. Special emphasis is placed on: (a) derivation of mouse strains and stocks of T1aa:hr genotype, to allow Qa-1 phenotyping of hr/hr and plus hr mice, (b) whether hr is fully recessive, or causes a minor syndrome in heterozygotes (special relevance to man), for which purpose congenic plus/plus mice are being bred; and (c) ranges of normal profile variation and profile change with age in the species.